Sauté sausage and onion together over medium-high heat, breaking sausage into pieces as it cooks. Once sausage is mostly browned, add garlic and carrot and continue cooking a minute longer.
Add chopped tomatoes, basil, and Italian seasoning and bring to a simmer. Reduce heat and simmer 10 minutes until tomatoes break down into a sauce.
Add kale, salt, and pepper and adjust seasonings to taste. Mix in spaghetti and half of parmesan. Add to casserole dish and sprinkle remaining parmesan on top.
Bake in preheated oven 20 - 30 minutes, until cheese is melted.